The invention relates to a local network comprising a plurality of network interfaces which are coupled each to a station and are provided for exchanging data with each other.
A local network is known from the publication "Ohne Chips nichts los"--Standard-Chips fur ATM-Systeme sind im Kommen, by Bernd Reder, Elektronik 1/1993, pages 66 to 75. This paper discusses the current situation of the development of integrated circuits used in local networks, which networks operate in the asynchronous transfer mode (ATM). Each station is then connected to the ring lines of the local network via a network interface. Switching devices (switches) are used in the network interfaces to control the ATM cell stream.
When an asynchronous transfer mode is used in a system, payload, for example, telephone, video or sound signals, is sent in blocks of fixed lengths through arrangements for digital signal processing. By a block of fixed length is meant a cell which contains a given number of bytes (for example, 53 bytes). Each cell contains a header field having a length of, for example, 5 bytes, and an information field which accommodates the payload and has a length of, for example, 48 bytes. In such a header field are available routing identification codes, error recognition data and control data. Routing identification codes are meant to be understood as trunk identifiers and connection identifiers. The connection identifier, also referenced VCI (Virtual Channel Identifier), contains the description of the destination of the cell in the system. To transmit a cell, a virtual channel is made available in response to the virtual channel identifier. As a rule, a VCI is changed each time a switching point is reached. A trunk group of various virtual channels is referenced a virtual path. A virtual path is identified by the trunk identifier. Such a virtual path is called a virtual path identifier (VPI). Cells are assigned to consecutively determined periods of time. The length of such a period of time depends on the clock rate used as a basis of the transfer components. If no payload is available, empty cells i.e. cells without payload, are transmitted in such a period of time. Cells containing payload are referenced payload cells.
For transmitting or exchanging data between the network interfaces of the local network, a cable-bound or a wireless type of radio communication can be selected. Data transmission via radio channels is advantageous, for example, if the station is to be mobile. Such a station is meant to be understood, for example, as a cordless telephone, a portable personal computer or wireless headphones.